However, i have new information for you. Neither the clipboard content nor the destination note is the problem. It's the editor's state! Obviously while editing notes (and also pasting/copy???) the editor state gets in trouble. I can not paste content into the editor. However, if i close and reopen the note pasting will success, though the content of the clipboard did not change.

For another test i left the editor window opened and removed all content. Still pasting was not possible. I exported the note to check, if there is some invisible content. The note does however match any other note, that gets created.